Quantifying normal ankle joint volume: An anatomic study

Many therapeutic and diagnostic modalities such as intraarticular injections, arthrography and ankle arthroscopy require introduction of fluid into the ankle joint. Little data are currently available in the literature regarding the maximal volume of normal, nonpathologic, human ankle joints. The purpose of this study was to measure the volume of normal human ankle joints.

A fluoroscopic guided needle was passed into nine cadaveric adult ankle joints. The needle was connected to an intracompartmental pressure measurement device. A radiopaque dye was introduced into the joint in 2 mL boluses, while pressure measurements were recorded. Fluid was injected into the joint until three consecutive pressure measurements were similar, signifying a maximal joint volume.

The mean maximum ankle joint volume was 20.9 +/- 4.9 mL (range, 16-30 mL). The mean ankle joint pressure at maximum volume was 142.2 +/- 13.8 mm Hg (range, 122-166 mm Hg). Two of the nine samples showed evidence of fluid tracking into the synovial sheath of the flexor hallucis longus tendon.

Maximal normal ankle joint volume was found to vary between 16-30 mL. This study ascertains the communication between the ankle joint and the flexor hallucis longus tendon sheath. Exceeding maximal ankle joint volume suggested by this study during therapeutic injections, arthrography, or arthroscopy could potentially damage the joint.